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270 4 Bacteria as Human Pathogens Lepromatous Leprosy- 270 4 Bacteria as Human Pathogens Lepromatous Leprosy- Fig.4.15 In lepromatous leprosy, nodular dermal and mucosal lesions develop. Nerve inflammation and neuroparalysis follow, eventually resulting in mutilations. Fig.4.15 In lepromatous leprosy, nodular dermal and mucosal lesions develop. Nerve inflammation and neuroparalysis follow, eventually resulting in mutilations. which no leprosy infection is present . The clinically differentiated...
Laboratory Diagnosis
Infections can be diagnosed either directly by detection of the pathogen or components thereof or indirectly by antibody detection methods. The reliability of laboratory results is characterized by the terms sensitivity and specificity, their value is measured in terms of positive to negative predictive value. These predictive values depend to a great extent on prevalence. In direct laboratory diagnosis, correct material sampling and adequate transport precautions are an absolute necessity....
Nontuberculous Mycobacteria NTM
Mycobacteria that are neither tuberculosis nor leprosy bacteria are categorized as atypical mycobacteria old designation , nontuberculous mycobacteria NTM or MOTT mycobacteria other than tubercle bacilli . Morphology and culture. In their morphology and staining behavior, NTM are generally indistinguishable from tuberculosis bacteria. With the exception of the rapidly growing NTM, their culturing characteristics are also similar to TB. Some species proliferate only at 30 C. NTM are frequent...
Plasmodium falciparum
Infected erythrocyte size and form normal, multiple infection more frequent than with other Plasmodium species, rarely Maurer's clefts Small rings 1 3 to 1 5 of EDM, binuclear form frequent, narrow plasmic fringe, vacuole small Vacuoles small or lacking, pigment dispersed or in clumps 8-24 merozoites, sometimes more, pigment usually peripheral Sickle-shaped, nucleus compact and central, pigment arranged around nucleus Sickle-shaped, plumper than D, nucleus larger and less compact Small rings 1...
The History of Infectious Diseases The Past
Infectious diseases have been known for thousands of years, although accurate information on their etiology has only been available for about a century. In the medical teachings of Hippocrates, the cause of infections occurring frequently in a certain locality or during a certain period epidemics was sought in changes in the air according to the theory of miasmas. This concept, still reflected in terms such as swamp fever or malaria, was the predominant academic opinion until the end of the...
Mechanisms of Action
When microorganisms are killed by heat, their proteins enzymes are irreversibly denatured. Ionizing radiation results in the formation of reactive groups that contribute to chemical reactions affecting DNA and proteins. Exposure to UV light results in structural changes in DNA thymine dimers that prevent it from replicating. This damage can be repaired to a certain extent by light photoreactivation . Most chemical agents alcohols, phenols, aldehydes, heavy metals, oxidants denature proteins...
General Aspects of Medical Microbiology
Infectious diseases are caused by subcellular infectious entities prions, viruses , prokaryotic bacteria, eukaryotic fungi and protozoans, metazoan animals, such as parasitic worms helminths , and some arthropods. Definitive proof that one of these factors is the cause of a given infection is demonstrated by fulfillment of the three Henle-Koch postulates. For technical reasons, a number of infections cannot fulfill the postulates in their strictest sense as formulated by R. Koch, in these...
Coronavirus Replication and Viral Maturation
The coronavirus genome consists of the longest known, sense RNA strand exceeding 30 kb, which is integrated in the envelope in the form of a helical ribonu-cleoprotein. A hallmark of coronaviral RNA replication is the production of seven subgenomic mRNAs, each of which codes for one viral structural protein. The synthesis of progeny viral RNA takes place in association with specialized membrane structures, characterized as double-membrane vesicles. Viral maturation takes place in the rough...
Streptococcus agalactiae B Streptococci
B streptococci occasionally cause infections of the skin and connective tissues, sepsis, urinary tract infections, pneumonia, and peritonitis in immunocom-promised individuals. About one in 1000 neonates suffers from a sepsis with or without meningitis. These infections manifest in the first days of life early onset type or in the first weeks of life late onset type . In the early onset form, the infection is caused intra partum by B streptococci colonizing the vagina. Potential predisposing...
Borrelia that Cause Relapsing Fevers
Taxonomy and significance. The genus Borrelia belongs to the family Spir-ochaetaceae. The body louseborne epidemic form of relapsing fever is caused by the species B. recurrentis. The endemic form, transmitted by various tick species, can be caused by any of a number of species at least 15 , the most important being B. duttonii and B. hermsii. Morphology and culture. Borreliae are highly motile spirochetes with three to eight windings, 0.3-0.6 im wide, and 8-18 im in length. They propel...
The Principies of Antibiotic Therapy
Specific antibacterial therapy refers to treatment of infections with anti-infective agents directed against the infecting pathogen. The most important group of anti-infective agents are the antibiotics, which are products of fungi and bacteria Streptomycetes . Anti-infective agents are categorized as having a broad, narrow, or medium spectrum of action. The efficacy, or effectiveness, of a substance refers to its bactericidal or bacteriostatic effect. Anti-infective agents have many different...
Hepatoviruses Hepatitis A Virus
Pathogen. The hepatitis A virus differs in some characteristics from entero-viruses, to which group it was long considered to belong. Growth in cell cultures requires long adaptation. Only one serotype is known to date. Pathogenesis and clinical picture. The clinical picture of hepatitis A, so-called epidemic or infectious hepatitis, differs in no major particulars from that of hepatitis B p. 429 . The disease nearly always takes a benign course. Only a small number of fulminant and sometimes...
Exotoxins
Enterotoxins disturb the normal functioning of enterocytes. Stimulation of adenylate or guanylate cyclase increased production of cAMP see p. 298 . This results in the loss of large amounts of electrolytes and water. Cytotoxins exert a direct toxic effect on cells enterocytes, endothelial cells . Endotoxin. Toxic effect of lipoid A as a component of LPS p. 156 . Serum resistance. Resistance to the membrane attack complex C5b6789 of the complement system p. 86ff. . Phagocyte resistance. Makes...
Tumor Immunity
Our knowledge concerning the immune control of tumors is still modest. Some tumor types bear defined tumor-associated, or tumor-specific, antigens. However this is apparently not sufficient for induction of an efficient immune defense. There is also the problem of tumor diagnosis the presence of tumors is sometimes confirmed using a functional or immunological basis, yet the tumor cannot be located because conventional examinations are often unable to discover them until they reach a size of...
Forms of Postnatal Toxoplasma Infection
Primary infection in immunocompetent persons. This is the most frequent form without clinical manifestations, recognizable by the specific serum antibodies. The infection can persist for the life of the host, and it may exacerbate in response to immunosuppression. Subacute cervical lymphadenitis occurs in about 1 of infected persons. Primary infection during pregnancy. This may cause prenatal infection of the fetus and thus become a significant threat see prenatal toxoplasmosis p. 513 ....
Francisella tularensis Tularemia
F. tularensis bacteria are coccoid, nonmotile, Gram-negative, aerobic rods. They cause a disease similar to plague in numerous animal species, above all in rodents. Humans are infected by contact with diseased animals or ectoparasites or dust. The pathogens invade the host either through microtraumata in the skin or through the mucosa. An ulcerous lesion develops at the portal of entry that also affects the local lymph nodes ulceroglandular, glandular, or oculoglandular form . Via lymphogenous...
Neisseria meningitidis Meningitis Sepsis
Morphology and culture. Meningococci are Gram-negative, coffee-bean-shaped cocci that are frequently pleomorphic and have a diameter of 1 im Fig. 4.16b . They are nonmotile and feature a polysaccharide capsule. Growing meningococci in cultures requires mediums containing blood. A concentration of 5-10 CO2 encourages proliferation. Antigen structure. Serogroups A, B, C, D, etc. a total of 12 are differentiated based on the capsule chemistry. Epidemics are caused mainly by strains of serogroup A,...
Preface
Medical Microbiology comprises and integrates the fields of immunology, bacteriology, virology, mycology, and parasitology, each of which has seen considerable independent development in the past few decades. The common bond between them is the focus on the causes of infectious diseases and on the reactions of the host to the pathogens. Although the advent of antibiotics and vaccines has certainly taken the dread out of many infectious diseases, the threat of infection is still a fact of life...
Neisseria Moraxella and Acinetobacter
Neisseria are Gram-negative, aerobic cocci that are often arranged in pairs. They are typical mucosal parasites that die rapidly outside the human organism. Culturing on enriched nutrient mediums is readily feasible. Neisseria gonorrheae is the pathogen responsible for gonorrhea clap . Infection results from sexual intercourse. The organisms adhere to cells of the urogenital tract by means of attachment pili and the protein Opa, penetrate into the organism using parasite-directed endocytosis...
Flagella
Flagella give bacteria the ability to move about actively. The flagella singular flagellum are made up of a class of linear proteins called flagellins. Flagel- Fig.3.13 a Flagellated bacterial cell SEM, 13 000x . b Helical structure of bacterial flagella SEM, 77 000x . Fig.3.13 a Flagellated bacterial cell SEM, 13 000x . b Helical structure of bacterial flagella SEM, 77 000x . lated bacteria are described as monotrichous, lophotrichous, or peritrichous, depending on how the flagella are...
Taenia solium Pork Tapeworm
Causative agent of T. solium taeniosis and cysticercosis Occurrence. T. solium is mainly endemic in poorly developed regions of Central and South America, Africa, and Asia, with sporadic occurrence in the USA as well as western, eastern, and southern Europe. In Mexico, 0.1-7 of the rural population are carriers of the adult tapeworm and up to 25 of the pigs carry the cysticerci of T. solium. Imported human cases of cysticercosis are being diagnosed in increasing numbers in nonendemic regions...
Sarcoptes scabiei
Causative agent of scabies the itch, sarcoptic itch Infestation with Sarcoptes scabiei var. hominis causes human scabies, a condition characterized by pronounced pruritus, epidermal mite burrows, nodules, and pustules. Transmission is person to person. Various mite species that parasitize animals may also infest the human skin without reproducing, causing the symptoms of pseudoscabies. Occurrence. Scabies caused by Sarcoptes scabiei var. hominis does not occur frequently in Europe, although...
Campylobacter
Classification. For several years now, Campylobacter bacteria have been classified together with Arcobacter medically insignificant in the new family Campylobacteriaceae fam. nov. . The genus Campylobacter comprises numerous species, among which C. jejuni more rarely C. coli, C. lari as well as C. fetus have been observed as causative pathogens in human infections. Morphology and culture. Campylobacter are slender, spirally shaped rods 0.2-0.5 im thick and 0.5-5 im long. Individual cells may...
Strategies against Nonspecific Immunity
Establishment of a bacterial infection in a host presupposes the capacity of the invaders to overcome the host's nonspecific immune defenses. The most important mechanisms used by pathogenic bacteria are Antiphagocytosis see also Fig. 1.6, p. 23 . Capsule. Renders phagocytosis more difficult. Capsule components may block alternative activation of complement so that C3b is lacking ligand for C3b receptor of phagocytes on the surface of encapsulated bacteria. Microorganisms that use this strategy...
Streptococcus pyogenes A Streptococci
Morphology and culturing. Gram-positive cocci with a diameter of 1 im that form chains Fig. 4.3a . Colonies on blood agar Fig. 4.3b show -hemo-lysis caused by streptolysins see below . Fine structure. The murein layer of the cell wall is followed by the sero-group A carbohydrate layer, which consists of C substance and is covalently bound to the murein. Long, twisted protein threads that extend outward are anchored in the cell wall murein the M protein. A streptococci are classified in serovars...
Rhinoviruses
Pathogens. The genomic organization and replication system of the rhino-viruses 117 serotypes found to date generally match those of the enteroviruses, although they differ in that they are acid-sensitive and slightly denser. Pathogenicity and clinical picture. The rhinoviruses, the causative pathogens of the common cold, infect the mucosa of the nasopharyngeal space nose and throat . They remain strictly localized there and do not cause generalized infections. In rare cases, mainly in...
Rhabdoviruses
Among the rhabdoviruses, the lyssaviruses, genotypes 1-7, are human pathogens. They are transmitted by the bite of an infected animal in its saliva and infections, once fully manifest, are always lethal rabies, hydrophobia . The reservoir for type 1 is provided by wild animals in general foxes, etc. , bats sylvatic rabies , and, in Asia, dogs urban rabies . Types 2-7 are restricted to Europe, Asia, Africa, and Australia with their main reservoir in bats. Diagnosis direct detection with IF in...
Astrovirus and Calicivirus Hepatitis E
Astroviruses, measuring 28-30 nm and caliciviruses, 30-35 nm, are enteritis pathogens in small children. Human pathogens in these groups include the Norwalk virus and hepatitis E virus HEV . The latter occurs epidemically and endemically in Asian, Central American, and African countries. It is transmitted by the fecal-oral route, above all via drinking water, and causes relatively benign infections except in pregnant women. Hepatitis E is considered a traveler's disease. Isolated cases and...
Basic Principles of Immunology
Resistance to disease is based on innate mechanisms and adaptive or acquired immunity. Acquired immune mechanisms act in a specific manner and function to supplement the important nonspecific or natural resistance mechanisms such as physical barriers, granulocytes, macrophages, and chemical barriers lysozymes, etc. . The specific immune mechanisms constitute a combination of less specific factors, including the activation of macrophages, complement, and necrosis factors the early recognition...
Erysipelothrix rhusiopathiae
This bacterium is a slender, nonmotile, Gram-positive rod. E. rhusiopathiae causes a septic disease in pigs, swine erysipelas. The correlate in humans is now quite rare and is a recognized occupational disease. Following contact with infectious animal material, the pathogens enter body tissues through dermal injuries. After an incubation period of one to three days, the so-called erysipeloid a hivelike, bluish-red swelling develops at the site of entry. The lymph nodes are also affected. These...
General Rules Applying to Infection Defenses
Non-specific defenses are very important e.g., Toll-like receptors, IFNa P , and 'natural immunity' meaning not intentionally or specifically induced represented by natural antibodies, direct complement activation, NK cell and phagocytes, plays a significant role in all infections. However, much remains to be learned about their roles. Antibodies represent potent effector molecules against acute bacterial infections, bacterial toxins, viral re-infections, and in many cases against acute...
Enterococcus Enterococci
Enterococci are a widespread bacterial genus p. 220 normally found in the intestines of humans and other animals. They are nonmotile, catalase-nega-tive, and characterized by group antigen D. They are able to proliferate at 45 C, in the presence of 6.5 NaCl and at pH 9, qualities that differentiate them from streptococci. As classic opportunists, enterococci show only low levels of pathogenicity. However, they are frequently isolated as components of a mixed flora in nosocomial infections p....
Brucella Brucellosis Bangs Disease
Occurrence and classification. The genus Brucella includes three medically relevant species B. abortus, B. melitensis, and B. suis besides a number of others. These three species are the causative organisms of classic zoonoses in livestock and wild animals, specifically in cattle B. abortus , goats B. melitensis , and pigs B. suis . These bacteria can also be transmitted from diseased animals to humans, causing a uniform clinical picture, so-called undulant fever or Bang's disease. Morphology...
Cysticercosis
Causative agent and epidemiology. The metacestodes of T. solium, known as Cysticercus cellulosae, can colonize various human organs Fig. 10.8 and cause the clinical picture of cysticercosis. Infections occur under unhygienic conditions due to peroral ingestion of eggs stemming from the feces of tapeworm carriers exogenous autoinfection or alloinfection . It is assumed that oncospheres hatching from eggs released from gravid proglottids in the human digestive tract may also cause an infection...
Afipia felis
The bacterial species Afipia Armed Forces Institute of Pathology felis was discovered several years ago. At first, it appeared that most cases of cat scratch disease were caused by this pathogen. Then it turned out that the culprit in those cases was usually either B. henselae or B. clarridgeia and that Afipia felis was responsible for only a small number. Afipia felis and B. henselae cat scratch infections present with the same clinical symptoms. Most cases of A. felis infections clear up...
Trypanosoma cruzi
Causative agent of American trypanosomosis Chagas disease Occurrence. Human Chagas disease is endemic in Central and South America and is caused by Trypanosoma cruzi discovered in 1908 by Chagas . This parasite circulates in endemic sylvatic foci between vertebrates and insects reduviid bugs , the latter transmitting it to humans. Until a few years ago, the endemic area of Chagas disease extended from Mexico to southern Argentina. In recent years parasite transmission to humans has been reduced...
Togaviruses
The togavirus family Togaviridae comprises two genera. Alphavirus infections are transmitted by arthropods and are imported to central Europe mainly by travelers to tropical and subtropical countries. Their clinical pictures are variable, but almost always include joint pain arthralgias . The most important representative of the genus Rubivirus is the rubella virus, the causative agent in German measles. This normally harmless childhood disease can cause severe embryopathies during the first...
Tuberculosis Bacteria TB
History. The tuberculosis bacteria complex includes the species Mycobacterium tuberculosis, M. bovis, and the rare species M. africanum. The clinical etiology of tuberculosis, a disease long known to man, was worked out in 1982 by R. Koch based on regular isolation of pathogens from lesions. Tuberculosis is unquestionably among the most intensively studied of all human diseases. In view of the fact that tuberculosis can infect practically any organ in the body, it is understandable why a number...
Ascaris lumbricoides Large Roundworm
Occurrence. The human large roundworm occurs worldwide. The number of infected persons is estimated at 1.38 billion WHO, 1998 . The main endemic regions, with prevalence rates of approx. 10-90 , include countries in Southeast Asia, Africa, and Latin America. Autochthonous infections are rare in central Europe. Parasite and life cycle. The adult ascarids living in the small intestine ascaris worm are 15-40 cm in length, about as thick as a pencil and of a yellowish pink color Fig. 10.12 . The...
Pathogenesis and clinical picture
Coltiviruses. Colorado tick fever usually runs a mild course with fever, myalgias, nausea, and vomiting, rarely encephalitis. Reoviruses. Implication of these viruses in diseases is still uncertain. It appears they are capable of infecting the respiratory and intestinal tracts of children. The fact that they are also found very frequently in asymptomatic persons makes it difficult to correlate them with specific clinical pictures. Rotaviruses. In the mid-seventies these viruses were recognized...
Salmonella Gastroenteritis Typhoid Fever Paratyphoid Fever
All salmonellae are classified in the species Salmonella enterica with seven subspecies. Nearly all human pathogen salmonellae are grouped under S. enterica, subsp. enterica. Salmonellae are further subclassified in over 2000 serovars based on their O and H antigens, which used to be incorrectly designated as species. Typhoid salmonelloses are caused by the serovars typhi and paratyphi A, B, and C. The salmonellae are taken up orally and the invasion pathway is through the intestinal tract,...
Protozoa
General information on parasites. A parasite from the Greek word parasitos is defined as an organism that lives in a more or less close association with another organism of a different species the host , derives sustenance from it and is pathogenic to the host, although this potential is not always expressed. In the wider sense, the term parasite refers to all organisms with such characteristics. In medicine the term is used in a narrower sense and designates eukaryotic pathogens, which belong...
HostCell Reactions
Possible consequences of viral infection for the host cell Cytocidal infection necrosis viral replication results directly in cell destruction cytopathology, so-called cytopathic effect in cell cultures . Apoptosis the virus initiates a cascade of cellular events leading to cell death suicide , in most cases interrupting the viral replication cycle. Noncytocidal infection viral replication per se does not destroy the host cell, although it may be destroyed by secondary immunological reactions....
Bordetella Whooping Cough Pertussis
The genus Bordetella, among others, includes the species B. pertussis, B. parapertussis, and B. bronchiseptica. Of the three, the pathogen responsible for whooping cough, B. pertussis, is of greatest concern for humans. The other two species are occasionally observed as human pathogens in lower respiratory tract infections. Morphology and culture. B. pertussis bacteria are small, coccoid, nonmotile, Gram-negative rods that can be grown aerobically on special culture mediums at 37 C for three to...
Attachment Pili Fimbriae Conjugation Pili
Many Gram-negative bacteria possess thin microfibrils made of proteins 0.11.5 nm thick, 4-8 nm long , the attachment pili. They are anchored in the outer membrane of the cell wall and extend radially from the surface. Using these structures, bacteria are capable of specific attachment to host cell receptors ligand receptor, key keyhole . The conjugation pili syn. sex pili in Gram-negative bacteria are required for the process of conjugation and thus for transfer of conjugative plasmids see p....
Naegleria Acanthamoeba and Balamuthia
Causative agents of naegleriosis, acanthamebosis, and balamuthiosis Free-living ameba of the genera Naegleria, Acanthamoeba, and Balamuthia have the potential to infect vertebrates and to cause diseases in humans. The morphological characteristics of these amebas include nucleus with large karyosome, lack of chromatin granules at the nuclear membrane see Entamoeba . Trophozoites Naegleria fowleri 15-30 im with wide pseudopods, produces flagellated stages in water Acanthamoeba spp. 24-56 im with...
Primary Mycoses
Primary systemic mycoses include histoplasmosis Histoplasma capsula-tum , North American blastomycosis Blastomyces dermatitidis , coccidioidomycosis Coccidioides immitis , and South American blastomycosis Paracoccidioides brasiliensis . The natural habitat of these pathogens is the soil. Their spores are inhaled with dust, get into the lungs, and cause a primary pulmonary mycosis. Starting from foci in the lungs, the organisms can then be transported, hematogenously or lymphogenously, to other...
Adaptive Immunotherapy
This involves in-vitro antigen stimulation, and consequent proliferation, of patient T-cell effector clones or populations CD8 T cells or less specific lymphokine-activated killer cells, LAK cells , followed by transfusion of these cells back into the patient. This method is sometimes used as a means of limiting cytomegaly or Epstein-Barr virus infection of bone marrow recipients. The LAK cells also include less specific NK-like cells, which can be expanded with 1L-2 in the absence of antigen...
Dicrocoelium dendriticum Lancet Liver Fluke
The lancet liver fluke 0.5-1.0 x 0.2 cm Fig. 10.6b , a bile duct parasite in sheep, cattle, and other herbivores, occurs frequently in regional foci in the northern hemisphere for instance southern Germany, Austria, Switzerland, North America . Its life cycle includes two intermediate hosts terrestrial snails and ants . Humans become infected accidentally when they ingest ants containing infective metacercariae of the lancet liver fluke. Such infections are rare and either run an asymptomatic...
Lice Anoplura
Causative agents of pediculosis and phthiriosis louse infestations Head lice and crab lice occur more frequently in central Europe and elsewhere than is generally assumed and must therefore always be taken into consideration when diagnosing skin diseases. Parasite species. Two species of lice infest humans, one of which is divided into two subspecies Table 11.3 . General morphology and biology. Lice are dorsoventrally flattened insects, about 1.5-4 mm in length, wingless, with reduced eyes,...